Significant advances have been made in the development of a new generation of molecularly targeted cancer drugs, many of which are only now emerging from the drug development pipeline. Examples of small molecule drugs are imatinib (Gleevec), used to treat CML, and gefinitib (Iressa), used to treat lung cancer. Other drugs, such as cetuximab (Erbitux) for colorectal cancer, are monoclonal antibodies. All of these drugs selectively modulate the activity of specific target proteins such as BCR-ABL tyrosine kinase (imatinib) and EGFR (gefitinib and cetuximab) that are critical for the proliferation and survival of cancer cells. However, clinical studies are revealing that patients often develop drug resistance due to overproduction or mutant forms of the target protein. For this reason, it is likely that future treatment with single or multiple targeted cancer drugs will require testing for preexisting or acquired resistance at the level of the target protein. The principal objective of this proposal is to develop and evaluate a sensitive and low cost technology known as PC-SNAG for monitoring resistance, to one or more drugs, in patients at the level of individual target proteins. A key feature of PC-SNAG is the ability to rapidly isolate native/active proteins from crude biological samples using photocleavable antibodies (PC-antibodies). During Phase I, proprietary high efficiency photocleavable linkers will be used to produce PC-antibodies immobilized on beads or other solid surfaces. The PC-antibodies are used to isolate and concentrate the target proteins from a heterogeneous biological sample. The target protein is then rapidly and gently photo released into solution in a native and highly pure form for functional analyses in the presence of drug. PC-SNAG facilitates a number of high throughput, sensitive functional assays that will be evaluated to detect resistant forms of the drug target and to determine optimal drug therapy on a per patient basis. In Phase I, the technology will be tested using model kinase-directed small molecule and antibody drugs followed by a focus on detection of drug resistant forms of the BCR-ABL tyrosine kinase. One goal is detection of <5% of the resistant form of the target, which is difficult to achieve using conventional DNA sequencing. In Phase II, clinical evaluation of the technology will be performed in collaboration with Dr. Daniel Wright, Chief of Hematology/Oncology at the Boston University Medical Center.